The present invention generally relates to a filter and more particularly, to a filter device of a helicopter blade tracker.
After maintenance has been performed on a helicopter, the blades must be positioned within predetermined tolerance limits. Conventionally, the positions of the blades are determined by a helicopter blade tracker which is mounted on a fuselage of the helicopter and orients upwardly toward the underside of the blades. The helicopter blade tracker views each of the blades through a narrow window and operates on the principle that a high-flying blade remains in the field of view longer than a low flying blade.
A discrepancy of this conventional practice in determining the positions of the blades is that when the helicopter blade tracker operates in, for example, direct and bright sunlight, the accuracy of it may be substantially reduced so that the positions of the blades may not be properly tracked.
As can be seen there is a need for improving the detection of blade position in a helicopter blade tracking system.